Recent content by ylem

Thank you all very much for your help. :-) However, how could I tell if a process is possible for on-shell particles? So... picking a simple process a photon annihilating to give an electron and positron. How can I determine if this is possible for on-shell particles? Cheers, Samantha

This is right. The reason it's a trace is because the definition of the trace is the sum of all the diagonal elements, Tr A = Sum A_{ii} (Sorry, I don't know how to get Latex stuff on here!). So, you have the same index at the start and the end of your T-matrix element, that's why it's a trace...

What do we mean when we say "on shell" particles? Hello! What do we mean when we say a particle in on shell? What is off shell? I gather it is related to energy and momentum conservation to say if a process is possible, but I've no idea what it actually is. Is it something to do with...

Hello! I was wondering if someone could help me with a problem of units! I'm currently deriving probability equations for neutrino oscillations and I'm stuck with units! I have: [(mass)^2 * time]/[4*energy] and I want to write it as [1.27 * (mass)^2 * distance]/[Energy] with distance in...

Hello! I was just wondering something... Why is it that a negative pion always decays into a muon and antimuon neutrino? Why not an electron and antielectron neutrino? (and the same for a positive pion) Any answers would be grately appreciated :-) Samantha

Yeah! Thanks a lot :-)

Hello! I hope I've posted this in the correct section... I'm a 3rd year undergraduate and we're currently studying Vector Spaces (in QM) and I just don't understand what injective (one-to-one) and surjective (onto) mean? As a result I have no idea what an isomorphism is! I realize this is...

Thanks! That's really helpful! :-) x

Thanks so much for your help! I think I understand it a bit more now! :-) x

Hey! I am completely confused... In quantum mechanics at University we are learning about operators. I don't understand what you actually have to do to write an operator as a matrix... In my notes, I'm looking at the kinetic energy operator in the Hamiltonian... I can see for something...

Is it not something to do with the fact that light does not have a wavelength small enough for us to see the spaces, as they're so small... so we have to use gamma rays ones and what not? I really have no clue... just guessing!

I have a few questions about Neutrino Oscillations... Firstly, why are they called oscillations? Is it because they can go back and forth to different flavours/masses? Next, if, for example, a tau neutrino is produced in the sun, will it oscillate to the other flavours on its way to earth...

Thanks! This is where I'm getting confused though, because if the y components cancel then when I find the magnitude of the field I will just be squaring the x components, so I won't have anything to the power of a half to expand using the Binomial? :confused:

Hello! Just hoping for a bit of help on a homework problem I'm doing at the moment... Basically this is the question: Three point charges are placed along the y axis: a charge q at y=a, a charge -2q at the origin and a charge q at q=-a. Such an arrangement is called an electric...

Hello! I have no idea here, I've just finished A-Levels, so I don't know a great deal about Physics at the mo, but I think I did some work experience on photocells... Just quoting Danger, but when the photons knock electrons out of orbit and they make a current, isn't it just a case of, when...